A pulse electric power amplification device is known. The pulse electric power amplification device includes, for example, a plurality of field-effect transistors (hereinafter referred to as FETs) used as electric power amplification elements cascade-connected in multiple stages.
FIG. 1 illustrates an example of a pulse electric power amplification device having this configuration. For example, an initial stage amplification device 53a, a second stage amplification device 53b, and a final stage amplification device 53c constituted of FETs are cascade-connected between an input terminal 51 and an output terminal 52. A switching circuit 55 switches a positive bias power supply 59 with a modulation pulse applied to a pulse input terminal 54, and supplies the result to amplification devices 53a, 53b, 53c as a positive operation power supply voltage. The modulation pulse received by the pulse input terminal 54 is also supplied to a differentiating circuit 56.
The differentiating circuit 56 differentiates a leading edge of the modulation pulse with a predetermined time constant, and gives a differentiation signal to an adding circuit 57. The adding circuit 57 adds the differentiation signal supplied by the differentiating circuit 56 to a negative bias voltage supplied by a negative bias power supply 58, and supplies the result to each amplification device other than the final stage amplification device 53c as an input side negative bias voltage. The voltage of the negative bias power supply 58 is simply supplied to the negative bias voltage terminal at the input side of the final stage amplification device 53c. 
When this pulse electric power amplification device receives a high frequency signal serving as an original signal of a transmission pulse received from the input terminal 51, the amplification devices 53a, 53b amplify the pulse within a time corresponding to a pulse width received from the pulse input terminal 54, and this increases the channel temperature of each amplification device, and the amplification gain decreases according to a predetermined thermal time constant. A signal differentiated with the thermal time constant is given from the differentiating circuit 56 to the adding circuit 57, in which the signal is added to the negative bias voltage, and the result is supplied to the amplification devices 53a, 53b other than the device in the final stage. In this manner, change of the amplification gain in a pulse over time is compensated in each amplification device.
When the power supply of the amplification device is supplied as a pulse wave in the pulse amplification apparatus, and the semiconductor devices of the same type are used as the amplification elements of the respective amplification devices, the amplification elements have almost the same thermal time constant, and therefore, change of the amplification gain over time can be compensated using a differentiating circuit having the same time constant.
By the way, a pulse amplification apparatus attracts attention. In this pulse amplification apparatus, GaAs is used in the upstream stage of the initial stage, and GaN is used in the downstream stage thereof, or SiGe is used in the upstream stage, and GaAs is used in the downstream stage, as amplification elements of respective amplification devices in order to achieve high output and high efficiency at the same time. The amplification device using GaAs, GaN, SiGe as the amplification elements have different thermal time constants at which the amplification gains decrease, which cannot be compensated with the same differentiating circuit.
In the pulse amplification apparatus in which the amplification devices using the different semiconductor devices in the upstream stage and the downstream stage of the initial stage unit are cascade-connected as described above, thermal time constants of these amplification devices are different. In this case, change of the amplification gain over time as shown in FIG. 1 cannot be compensated, and the phase change within a pulse deteriorates, which makes it impossible to obtain the pulse amplification apparatus having highly linear amplification characteristics.
The present invention provides a pulse amplification apparatus in which amplification devices using semiconductor devices having different properties in an upstream stage and a downstream stage of an initial stage unit are cascade-connected as described above, wherein change of an amplification gain over time with a thermal time constant can be compensated, so that the pulse amplification apparatus has high degree of linearity.